Sustainability of Crop Residues and Manure Management in Smallholder Cereal-Legume-Livestock Systems in the Savannas of West Africa
The integration of crops and livestock is an effective means of harnessing and recycling nutrients in manure and crop residues to improve crop yields. However, the competing demands for crop residues within the farm present a tradeoff between increasing crop yields and sustaining livestock productivity. The effectiveness of manure as fertiliser on the other hand is constrained by poor handling and storage techniques. This thesis addresses the challenges associated with crop residues and manure management in five studies: i) assessment of nutrient balances, ii) quantification of tradeoffs, iii) appraisal of the sustainability of crop residue uses, iv) evaluation of manure management options and v) quantification of added benefits from integrated use of mineral fertiliser and manure. The NUTMON framework was used to assess the N and P balances in cereal-legume-livestock farms at Cheyohi, Ghana (Ferric Luvisols), Sarauniya, Nigeria (Regosols) and Garin Labo, Niger (Eutric Gleysols). Nitrogen balances ranged from -7 to -22 kg ha-1 with the application of the recommended N rate and -34 to -82 kg ha-1 in the absence of fertiliser use. The application of the recommended rate of P led to the P accumulation in the order of 3 to 7 kg ha-1. However, without the application of fertiliser, P depleted at rate of 2 to 7 kg ha-1 annually. The tradeoffs for allocating crop residues between the crop and livestock units of the farm were evaluated by incorporating 0, 25, 50, 75, and 100 % of haulm and stover yield of the farm into the soil and feeding the remaining amount to small ruminants. The tradeoffs estimates favoured the incorporation of 75 % haulm and 25 % stover at Cheyohi, 25 % haulm and 75 % stover at Sarauniya, and 0 % haulm and 0 % stover at Garin Labo. An agricultural sustainability index was used to appraise the sustainability of the five management scenarios. The use of 75 % of haulm and 25 % of stover as soil amendment was found to be the most sustainable option in Farm 1 at Cheyohi. Other sustainable options were, the total removal of crop residues in Farm 1 at Sarauniya and Garin Labo, and the use of 75 % of haulm and 25% of stover as soil amendment in Farm 2 at Sarauniya. The effects of oil cakes and manure storage methods on nutrient losses during composting were evaluated at Nyankpala, Zaria and Maradi. The storage of manure in heaps or pits and fortification with oil cake had no effect on N and P losses during composting at all locations. The use of plastic sheets to cover heaps or line pits significantly reduced N losses from 29 – 67 % to 5 – 30 % and P losses from 25 – 37 % to 2 – 20 % at Nyankpala and Zaria but had no effect on nutrient losses at Maradi. The added benefits and economic returns from the combined application of mineral fertiliser and manure were evaluated at Nyankpala, Sarauniya and Maradi. Added benefits in grain yield ranged from -68 to 470 kg ha-1 at Nyankpala and -514 to 684 kg ha-1 at Sarauniya. No added benefits were found at Maradi. The most cost effective application rates were 2.5 t ha-1 of manure complemented with either 25 % of the fertiliser recommendation at Nyankpala or 50 % of the fertiliser recommendation at Sarauniya.
A thesis submitted to the Department of Crop and Soil Sciences, Faculty of Agriculture, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements of the degree of DOCTOR OF PHILOSOPHY In Soil Science,2011